The present invention relates to interface pickups and, more particularly, to a contactless inductance interface pickup designed especially for use in electric-metal-lurgical installations for smelting metals and metal alloys, as well as in electroslag welding facilities.
The interface of two media differing in specific density and resistivity of which at least one is electrically conductive and non-magnetic, maybe determined with the use of contactless and contact pickups.
The contact interface pickups are formed as a horizontal cooled probe and a vertical cooled probe. The horizontal cooled probe is disposed in the forming wall, a crystallizer or a welding shoe, and is electrically insulated from the wall. With the probe so disposed, the slag-metal interface may be determined. The vertical cooled probe is disposed in the forming wall above the fluid slag to determine the air-fluid slag interface. Voltage from an independent source is impressed on the probes and on the ingot being cast or on the workpiece being welded. As soon as the current through the probe-metal or the probe-fluid slag circuit reaches the metal bath or the fluid slag, its magnitude sharply increases, indicating the interface of the two media.
These pickups, however, have a major disadvantage in that the operation of the pickups depends by and large on the rate of coolant consumption. As the coolant consumption increases, slag particles adhere to the probe end and solidify, forming an obstruction to the passage of electric current. As the coolant consumption decreases, the probe melts which gives rise to an emergency situation, for liquid finds ingress into the fluid slag or the metal bath. Another serious disadvantage of contact pickups prohibitive to their large-scale application is that layers of molten metal are formed between the horizontal probe and the metal bath which, upon solidification, short out the probe-metal circuit.
One prior art contactless inductance interface pickup is an attachable contactless inductance pickup which comprises two energized windings disposed on the extreme poles of a magnetic circuit and a measuring winding disposed on the central pole. Between one of the extreme poles of the magnetic circuit and its central pole, a vessel is disposed containing two media whose interface is to be determined.
The attachable pickup determines the air-molten metal interface when placed at the wall of a pot or ladle. However, it cannot be employed in the processes of electroslag, plasma-arc and electron-beam remelting or in electroslag welding, for such a pickup can only operate when the vessel containing the two media whose interface to be determined is constructed from a non-magnetic material.
It is likewise known to employ a contactless interface pickup for determining the interface of two media differing in specific density and resistivity of which at least one is electrically conductive and non-magnetic. This pickup has a cooled housing with a cover which houses an open magnetic circuit with at least one measuring winding and an energized winding, the poles of the magnetic circuit being oriented toward the interface to be determined.
The magnetic circuit of the pickup is trident-shaped, and its energized and measuring windings are poled in opposition. Since the magnetic circuit with its windings must be disposed in immediate proximity to the interface, the housing within which the magnetic circuit is disposed is to be cooled with a cooling agent. In order to protect the windings and the magnetic circuit against the cooling agent, they are embedded in a cold-curing epoxy resin. However, the embedding procedure fails to pressurize the sites where the leads of the windings extend through the resin and out of the housing.
Another disadvantage of this latter known pickup is the difficulty in controlling the clearance between the magnetic circuit poles and the bottom of the housing, i.e. the interface of the two media, which is required due to the imbalance of the zero signal. This difficulty stems from the fact that the magnetic circuit cannot be moved inside the housing in the course of operation without cutting off the coolant supply; and should the coolant supply be interrupted even for a short time, the pickup housing comes into direct contact with molten metal, which renders the pickup inoperative.
There is still a further disadvantage, viz. cracking of the resin in which the magnetic circuit is embedded due to the sharp fluctuations of the heat load, with the result that the coolant finds ingress to the windings, shorting them out.